1. Field of the Invention
The invention relates generally to a table or workbench covering which is electrically conductive. In particular, the invention is a cover made of a first electrically conductive layer having a specific resistance in the range of 5×106 Ωcm to 5×109 Ωcm, and a second electrically conductive layer having a specific resistance of 5×104 to 5×107 Ωcm, which are each made of rubber mixtures, and which contain antistatic agents and/or electrically conductive particles, as well as being connected by calendering and vulcanization.
2. Description of Related Art
Table coverings used in the electronics industry have two essential functions. On the one hand, because of their specific resistance they are in a position to make harmless electrostatic charges of tools, by their electrical discharging capability, and on the other hand their surface is intended to avoid mechanical damage to parts being worked on on the surface. Two-layer table coverings having a typical leakage resistance RG of 104×107Ω are known from the brochure of the Firm Warmbier. In view of the increasing demands on the storage density of hard disks, increasingly great requirements are being set with respect to production free from contamination. This is particularly so with regard to ionic contamination, which, in conjunction with moisture, may cause corrosion on the hard disks. Sulfate-ions have proven troublesome, among others. Up to the present, rubber table coverings have demonstrated sulfate values of an order of magnitude of 200-800 μg/cm2 of covering surface, which is determined by extraction using deionized water and ion chromatography.